How to Define Malnutrition
Parameters used to define malnutrition/undernutrition vary in most studies, thus underscoring the need to establish a standard set of criteria to define adult malnutrition. Historically, clinicians used serum protein levels, including albumin and prealbumin, to determine nutritional status. However, current research indicates that serum protein levels may be affected by inflammation, renal function, hydration, and other factors.12 During periods of inflammatory stress, albumin and prealbumin levels drop because they are negative acute-phase reactants. In response, there is an increase in cytokines, including interleukin 1β, interleukin 6, and tissue necrosis factor, causing the liver to synthesize positive acute-phase reactants rather than negative acute-phase reactants. Inflammatory biomarkers, such as C-reactive protein, ferritin, and other positive acute-phase reactants, quickly rise with acute inflammation and decline as inflammation diminishes. Inflammation may be a contributing factor when C-reactive protein levels increase, and albumin and prealbumin levels decline.12,13
Several studies reported evidence suggesting that serum hepatic proteins correlate with mortality and morbidity, are useful indicators of illness severity, and help to identify individuals at risk for developing malnutrition.14–18 Hepatic protein levels do not accurately measure nutritional repletion18; thus, serum concentrations may not be markers of malnutrition or caloric repletion. As of 2012, the Academy of Nutrition and Dietetics (Academy) and American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.) do not recommended using inflammatory biomarkers such as serum protein levels for diagnosis of malnutrition.18
“Adult undernutrition typically occurs along a continuum of inadequate intake and/or increased requirements, impaired absorption, altered transport, and altered nutrient utilization,”18 states the Academy and A.S.P.E.N.
Weight loss may occur at various points along this continuum. Inflammation appears to be the common thread in disease progression and concurrent declining nutritional status.19
Current evidence suggests that inflammation is an important underlying factor, and there are varying degrees of acute and chronic inflammation associated with injury, infection, and disease.12,18–22 Diseases such as diabetes mellitus, cardiovascular diseases, arthritis, and cancers produce chronic inflammation that is sustained and persistent. Elevated energy expenditure and catabolism of lean body mass are associated with chronic inflammation. Individuals with a critical illness, major infection, or traumatic injury may have a condition associated with an acute inflammatory response. This acute-phase inflammatory response triggers a sequence of reactions leading to elevated resting energy expenditure and nitrogen excretion, which increases energy and protein requirements concurrently with anorexia and pathologically altered utilization of nutrients.22
The body reacts with a suboptimal response, and nutrition interventions are not adequate to reverse the mobilization of nutrients and other cytokine-related changes in organ function. Jensen et al22 define the point at which the severity or persistence of inflammation leads to a decrease in lean body reserves linked to impaired functional status as disease-related malnutrition. Figure 1 describes etiology–based malnutrition definitions.
In 2009, A.S.P.E.N. and the European Society for Clinical Nutrition and Metabolism convened an International Consensus Guideline Committee to adopt an etiology-based approach to the diagnosis of adult malnutrition. The definitions developed and endorsed by A.S.P.E.N. and the European Society for Clinical Nutrition and Metabolism to describe adult malnutrition were accepted by the Academy. The definitions describe adult malnutrition in a framework of acute illness or injury, chronic disease or conditions (lasting >3 months), and starvation-related malnutrition.18 The identification of 2 or more of the following 6 characteristics is required for the nutrition diagnosis of malnutrition (also known as undernutrition): insufficient energy intake, weight loss, loss of muscle mass, loss of subcutaneous fat, fluid accumulation (that may mask weight loss), and/or diminished functional status (as measured by hand-grip strength).18
This etiology-based nomenclature takes into account the understanding of the role of the inflammatory response on incidence, progression, and resolution of malnutrition in adults. Adapting a standardized approach to diagnose malnutrition using these characteristics will lead to early identification of declining nutritional status, which impacts pressure ulcer prevention and healing.
Excerpt originally appeared in Advances in Skin & Wound Care. All credit to authors and Wolters Kluwer Health, Inc.